Added a new feature to disable wrapping of identifiers during proxy serialization

[jobosk]

Following issue #136, this PR is intended to add a new backswards-compatible feature, that allows serialization of lazy loaded objects as identifiers in numeric values, rather than wrapped in objects. The new Feature "WRAP_IDENTIFIER_IN_OBJECT" (i.e. current behaviour) is enabled by default (to avoid double negative), and can be disabled if desired.

[cowtowncoder]

I think PR looks good so the only thing I need is the Contributor License
Agreement (CLA) from:

https://github.com/FasterXML/jackson/blob/master/contributor-agreement.pdf

and I can merge this to be included in 2.12!

[jobosk]

I have just commited the Javadoc annotation.
Due to the COVID situation I'm somewhere where I dont have access to a printer all that easily, but I haven't forgot and I will send it ASAP

[cowtowncoder]

@jobosk No problem at all, and sorry about the hassle with CLA. My main concern is just that I don't forget to follow up on this, so whenever you can do that. There may be another way to convert CLA pdf to image file, then add text on other fields but scan signature (like write it on paper, take a photo, paste that on CLA image). I think some contributors have done that -- I wish I had better steps to suggest.